Recent developments in hematopoietic stem cell transplantation provide a new therapeutic opportunity for treating type 1 diabetes. The principal investigator and co-principal investigator, as bench-to-bedside partners, will develop a strategy to cure type 1 diabetes by combining hematopoietic stem cell transplantation with islet transplantation. Our specific approach is to induce mixed chimerism, using a relatively nontoxic protocol that is nonmyeloablative and irradiation-free, to abrogate the autoimmune processes leading to the onset of type 1 diabetes; and then to transplant a small number of donor-specific islets to achieve normoglycemia and insulin independence, thereby curing diabetes. At the clinical onset of type 1 diabetes, it is estimated that patients have about 20% of their beta cell mass remaining. We hypothesize that establishing mixed chimerism using our relatively nontoxic approach will abrogate further progression of type 1diabetes and preserve the remaining beta cell mass. Even if the remaining beta cell mass in the recipient's native pancreas is not sufficient to reverse diabetes, only a small number of transplanted islets should be enough to reverse diabetes in chimeric patients. Using MHC-matched, partially MHC-mismatched, and fully MHC-mismatched mice as hematopoietic stem cell and islet donors, we will determine whether the autoimmune processes leading to the development of type 1 diabetes can be reversed and whether remission can be induced in overtly diabetic NOD mice that mixed chimerism will be established through unmodified allogeneic bone marrow transplantation with our relatively nontoxic protocol. We will also determine whether T cell-depleted and purified hematopoietic cell transplantation can be as effective as unmodified bone marrow transplantation. Finally, we will determine whether normoglycemia can be achieved and be maintained by transplanting a small number of donor-specific islet mass into chimeric diabetic NOD mice, if their remaining islet mass is not sufficient to reverse diabetes. Our transplant team, led by Dr. Sutherland, co-principal investigator of this proposal, has successfully performed the largest number of living related segmental pancreas transplantation and islet autotransplantation worldwide. We have the capability to transplant donor-specific islets from living donors. Success in our proposed experiments, combined with our profound clinical experience, will provide a solid foundation for further development of a safe, effective, and clinically applicable approach for curing type 1 diabetes.